Usefulness as key parameter in assessing accessibility and usability in architecture. A theorem for explaining a twin concept in the building code

In national building codes, like the Danish and the Swedish ones, accessibility and usability are subjected to an open interpretation on a comprehensive level, supplemented by specified requirements on a detailed level. The aim of the pre­sent study is to position the twin concept with regard to its everyday understanding, and thereby suggest a definition. The study has been executed as a case study among a cohort of 370 experienced Danish professionals. The research material was assembled by use of mini-questionnaires. Conclusions derived from this material were synthesized with the respondents’ suggestions of exemplary models, which allegedly displayed an appropriate level of accessible and usable architecture and built environment. Based on the every­day understanding of the twin concept and paired with analyses of some exemplary models, this study suggests that accessibility and usability with respect to the user can be seen as constituents of buildings’ overall performative capacity. This capacity can be defined as usefulness, the potential sum of various adjustments of an accessible and usable nature. Ultimately, usefulness refers to the individual user’s level of independent usages of the particular architectural space.